DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Mercurial (b66b287a2650)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320
// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/shared_memory.h"

#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

#include "base/file_util.h"
#include "base/logging.h"
#include "base/platform_thread.h"
#include "base/string_util.h"

namespace base {

namespace {
// Paranoia. Semaphores and shared memory segments should live in different
// namespaces, but who knows what's out there.
const char kSemaphoreSuffix[] = "-sem";
}

SharedMemory::SharedMemory()
    : mapped_file_(-1),
      inode_(0),
      memory_(NULL),
      read_only_(false),
      max_size_(0) {
}

SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only)
    : mapped_file_(handle.fd),
      inode_(0),
      memory_(NULL),
      read_only_(read_only),
      max_size_(0) {
  struct stat st;
  if (fstat(handle.fd, &st) == 0) {
    // If fstat fails, then the file descriptor is invalid and we'll learn this
    // fact when Map() fails.
    inode_ = st.st_ino;
  }
}

SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only,
                           ProcessHandle process)
    : mapped_file_(handle.fd),
      memory_(NULL),
      read_only_(read_only),
      max_size_(0) {
  // We don't handle this case yet (note the ignored parameter); let's die if
  // someone comes calling.
  NOTREACHED();
}

SharedMemory::~SharedMemory() {
  Close();
}

// static
bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
  return handle.fd >= 0;
}

// static
SharedMemoryHandle SharedMemory::NULLHandle() {
  return SharedMemoryHandle();
}

#ifdef CHROMIUM_MOZILLA_BUILD
bool SharedMemory::Create(const std::string &cname, bool read_only,
#else
bool SharedMemory::Create(const std::wstring &name, bool read_only,
#endif
                          bool open_existing, size_t size) {
  read_only_ = read_only;

#ifdef CHROMIUM_MOZILLA_BUILD
  std::wstring name = UTF8ToWide(cname);
#endif

  int posix_flags = 0;
  posix_flags |= read_only ? O_RDONLY : O_RDWR;
  if (!open_existing || mapped_file_ <= 0)
    posix_flags |= O_CREAT;

  if (!CreateOrOpen(name, posix_flags, size))
    return false;

  max_size_ = size;
  return true;
}

// Our current implementation of shmem is with mmap()ing of files.
// These files need to be deleted explicitly.
// In practice this call is only needed for unit tests.
bool SharedMemory::Delete(const std::wstring& name) {
  std::wstring mem_filename;
  if (FilenameForMemoryName(name, &mem_filename) == false)
    return false;

  FilePath path(WideToUTF8(mem_filename));
  if (file_util::PathExists(path)) {
    return file_util::Delete(path, false);
  }

  // Doesn't exist, so success.
  return true;
}

bool SharedMemory::Open(const std::wstring &name, bool read_only) {
  read_only_ = read_only;

  int posix_flags = 0;
  posix_flags |= read_only ? O_RDONLY : O_RDWR;

  return CreateOrOpen(name, posix_flags, 0);
}

// For the given shmem named |memname|, return a filename to mmap()
// (and possibly create).  Modifies |filename|.  Return false on
// error, or true of we are happy.
bool SharedMemory::FilenameForMemoryName(const std::wstring &memname,
                                         std::wstring *filename) {
  std::wstring mem_filename;

  // mem_name will be used for a filename; make sure it doesn't
  // contain anything which will confuse us.
  DCHECK(memname.find_first_of(L"/") == std::string::npos);
  DCHECK(memname.find_first_of(L"\0") == std::string::npos);

  FilePath temp_dir;
  if (file_util::GetShmemTempDir(&temp_dir) == false)
    return false;

  mem_filename = UTF8ToWide(temp_dir.value());
  file_util::AppendToPath(&mem_filename, L"com.google.chrome.shmem." + memname);
  *filename = mem_filename;
  return true;
}

// Chromium mostly only use the unique/private shmem as specified by
// "name == L"". The exception is in the StatsTable.
// TODO(jrg): there is no way to "clean up" all unused named shmem if
// we restart from a crash.  (That isn't a new problem, but it is a problem.)
// In case we want to delete it later, it may be useful to save the value
// of mem_filename after FilenameForMemoryName().
bool SharedMemory::CreateOrOpen(const std::wstring &name,
                                int posix_flags, size_t size) {
  DCHECK(mapped_file_ == -1);

  file_util::ScopedFILE file_closer;
  FILE *fp;

  if (name == L"") {
    // It doesn't make sense to have a read-only private piece of shmem
    DCHECK(posix_flags & (O_RDWR | O_WRONLY));

    FilePath path;
    fp = file_util::CreateAndOpenTemporaryShmemFile(&path);

    // Deleting the file prevents anyone else from mapping it in
    // (making it private), and prevents the need for cleanup (once
    // the last fd is closed, it is truly freed).
    file_util::Delete(path, false);
  } else {
    std::wstring mem_filename;
    if (FilenameForMemoryName(name, &mem_filename) == false)
      return false;

    std::string mode;
    switch (posix_flags) {
      case (O_RDWR | O_CREAT):
        // Careful: "w+" will truncate if it already exists.
        mode = "a+";
        break;
      case O_RDWR:
        mode = "r+";
        break;
      case O_RDONLY:
        mode = "r";
        break;
      default:
        NOTIMPLEMENTED();
        break;
    }

    fp = file_util::OpenFile(mem_filename, mode.c_str());
  }

  if (fp == NULL)
    return false;
  file_closer.reset(fp);  // close when we go out of scope

  // Make sure the (new) file is the right size.
  // According to the man page, "Use of truncate() to extend a file is
  // not portable."
  if (size && (posix_flags & (O_RDWR | O_CREAT))) {
    // Get current size.
    size_t current_size = 0;
    struct stat stat;
    if (fstat(fileno(fp), &stat) != 0)
      return false;
    current_size = stat.st_size;
    // Possibly grow.
    if (current_size < size) {
      if (fseeko(fp, current_size, SEEK_SET) != 0)
        return false;
      size_t writesize = size - current_size;
      scoped_array<char> buf(new char[writesize]);
      memset(buf.get(), 0, writesize);
      if (fwrite(buf.get(), 1, writesize, fp) != writesize) {
          return false;
      }
      if (fflush(fp) != 0)
        return false;
    } else if (current_size > size) {
      // possibly shrink.
      if ((ftruncate(fileno(fp), size) != 0) ||
          (fflush(fp) != 0)) {
        return false;
      }
    }
  }

  mapped_file_ = dup(fileno(fp));
  DCHECK(mapped_file_ >= 0);

  struct stat st;
  if (fstat(mapped_file_, &st))
    NOTREACHED();
  inode_ = st.st_ino;

  return true;
}

bool SharedMemory::Map(size_t bytes) {
  if (mapped_file_ == -1)
    return false;

  memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
                 MAP_SHARED, mapped_file_, 0);

  if (memory_)
    max_size_ = bytes;

  bool mmap_succeeded = (memory_ != (void*)-1);
  DCHECK(mmap_succeeded) << "Call to mmap failed, errno=" << errno;
  return mmap_succeeded;
}

bool SharedMemory::Unmap() {
  if (memory_ == NULL)
    return false;

  munmap(memory_, max_size_);
  memory_ = NULL;
  max_size_ = 0;
  return true;
}

bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                        SharedMemoryHandle *new_handle,
                                        bool close_self) {
  const int new_fd = dup(mapped_file_);
  DCHECK(new_fd >= -1);
  new_handle->fd = new_fd;
  new_handle->auto_close = true;

  if (close_self)
    Close();

  return true;
}


void SharedMemory::Close() {
  Unmap();

  if (mapped_file_ > 0) {
    close(mapped_file_);
    mapped_file_ = -1;
  }
}

void SharedMemory::LockOrUnlockCommon(int function) {
  DCHECK(mapped_file_ >= 0);
  while (lockf(mapped_file_, function, 0) < 0) {
    if (errno == EINTR) {
      continue;
    } else if (errno == ENOLCK) {
      // temporary kernel resource exaustion
      PlatformThread::Sleep(500);
      continue;
    } else {
      NOTREACHED() << "lockf() failed."
                   << " function:" << function
                   << " fd:" << mapped_file_
                   << " errno:" << errno
                   << " msg:" << strerror(errno);
    }
  }
}

void SharedMemory::Lock() {
  LockOrUnlockCommon(F_LOCK);
}

void SharedMemory::Unlock() {
  LockOrUnlockCommon(F_ULOCK);
}

SharedMemoryHandle SharedMemory::handle() const {
  return FileDescriptor(mapped_file_, false);
}

}  // namespace base